This invention relates to a method for treating fuel contaminated wastewater. In a more specific aspect, this invention concerns itself with the ultraviolet light catalyzed chlorinolysis of hydrazine fuel-contaminated wastewater.
Facilities are presently available for the blending of various hydrazines to produce fuels for rocket and missile applications. The primary operation of these facilities involves blending, such as the mixing of hydrazine (N.sub.2 H.sub.4) with unsymmetrical dimethyl hydrazine (UDMH), cleaning of railway cars and storage tanks, as well as the cleaning and maintenance of production equipment and piping. During the manufacture, handling and storage of hydrazine based fuels, large amounts of fuel-contaminated wastewater are generated. Usually, the wastewater is transported to a pond, treated with hypochlorite to reduce the degree of contamination, and then pumped to a lake for permanent disposal. Oftentimes, however, the treated wastewater still contains several hundred parts per million of contaminants even though the hypochlorite was able to reduce the degree of contamination downwardly from the original degree of contamination which often exceeded 2800 ppm of hydrazine contaminants. As a consequence, the treated water still contained sufficient contaminants to constitute an environmental hazard. The hypochlorite treatment, therefore, is considered to be an unsatisfactory decontamination system. In addition to hydrazine contamination, the wastewater also contains low concentrations of dimethylnitrosamine (DMNA) which is present in UMDH fuel as an impurity and as an undesirable reaction by-product formed during exposure of UDMH to oxygen in the presence of light. The presence of monomethyl hydrazine (MMH), another fuel component, is also found to be present in wastewater emanating from rocket fuel production facilities.
It is particularly important, therefore, that a wastewater treatment system be developed that can effectively decontaminate wastewater contaminated by N.sub.2 H.sub.4, DMNA, MMH and UDMA. The need for a treatment process that is safe, reliable, inexpensive and ecologically acceptable becomes obvious when one considers the environmental dangers involved in discharging contaminated wastewater into our surrounding environs. As a result of this need, a great deal of consideration and research effort has been given to a variety of physical and chemical decontamination treatment methods for the removal of UDMH, MMH, N.sub.2 H.sub.4 and DMNA from wastewater. The particular methods researched, and the results achieved by resorting to such methods, all suffer some disadvantages. An outline of the prior art methods and their disadvantages with respect to the decontamination of UDMA, MMH, N.sub.2 H.sub.4 and DMNA contaminated wastewater having at least 2800 ppm decontaminants are shown in Table I.
TABLE I __________________________________________________________________________ TREATMENT OF HYDRAZINE-CONTAINING WASTE WATERS Treatment Method MMH UDMH N.sub.2 H.sub.4 DMNA __________________________________________________________________________ Ozone destroys Makes DMNA *N.D. no reaction Oxidation destroys destroys--makes N.D. no reaction colored reaction product Biological Max. 10 ppm Max. 10 ppm N.D. Max. 10 ppm Degradation Carbon Very little Very little N.D. Very little Adsorption adsorption adsorption adsorption NaOCl poor at high pH OK at all pH's N.D. N.D. OK at low pH H.sub.2 O.sub.2 destroys Makes DMNA N.D. N.D. Chloride erratic results OK at all pH's OK at all OK at low pH at high pH; pH's with large OK low pH excess of chlorine Chlorine and OK at all pH's OK at all pH's N.D. OK at all pH's UV light __________________________________________________________________________ *N.D.--not determined
These results indicate that chlorine will readily react with all four substances at low pH in the presence of an excess of chlorine. The major shortcoming of the systems studied, however, was their inability to decompose DMNA. DMNA was in fact produced by the reaction of UDMH with ozone and peroxide. Therefore, it was concluded that chlorinolysis of the wastewater could only be accomplished at low pH. Unfortunately, decontamination procedures that operate at a low pH of about 1.5 have a deleterious and corrosive effect on equipment and piping and require extensive neutralization procedures before disposing of the treated hydrazine contaminated wastewater.
In further attempts at providing a solution to the problem of decontaminating hydrazine containing wastewater, as well as attempting to comply with the objections of treating wastewater containing specific contaminants of about 1-100 ppm DMNA, 50-500 ppm MMH, 100-3000 ppm UDMH, and 100-3000 ppm N.sub.2 H.sub.4, it was unexpectedly found that a solution to the aforestated problem could be provided by a treatment method which involves the ultraviolet light (UV) induced chlorination of contaminated wastewater at a controlled pH of about 5. This procedure, conducted at a reasonably high pH, also overcomes the corrosion problems encountered when using the low pH methods of the past. The wastewater treatment system of this invention has been found to be capable of discharging a decontaminated wastewater to a sanitary wastewater system with a maximum of only 0.1 ppm of each of the four pollutants, MMH, UDMH, N.sub.2 H.sub.4 and DMNA. It has been established that these materials are bio-degraded when in concentrations of less than 10 ppm. Thus, the effluent from the sanitary wastewater system of this invention will be well below current detection limits and will not present a toxic or ecological hazard.